Catalytic converter structures with electrohydrodynamic heat and mass transfer

ABSTRACT

A catalytic converter assembly has a ceramic substrate body with a plurality of cells for passage therethrough of exhaust gases. An emitter electrode for emitting free electrodes is mounted adjacent the substrate body for intercepting exhaust gas flowing at an upstream location of the catalytic converter. A collector electrode for collecting electrons is mounted adjacent the substrate body to intercept exhaust gas flowing at a downstream location of the catalytic converter. An energizing circuit is used to apply a high voltage between the emitter and collector to stimulate the generation of free electrons.

CROSS REFERENCE TO RELATED PATENTS

The present application claims priority pursuant to 35 U.S.C. §119(e) topending U.S. Provisional Application Ser. No. 61879211 entitled“Catalytic converter employing electrohydrodynamic technology” filedSep. 18, 2013, and pending U.S. Provisional Application Ser. No.61910067 entitled “Catalytic converter employing electrohydrodynamictechnology” filed Nov. 28, 2013, the disclosure of which applicationsare hereby incorporated herein by reference in their entirety and madepart of the present application for all purposes.

FIELD OF THE INVENTION

This invention relates to a structures and methods of operation ofcatalytic converters for treating exhaust gases to reduce harmfulpollution and has particular but not exclusive application to reducingpollution from internal combustion engines at start-up and when idling.

BACKGROUND

The U.S. Department of Transportation (DOT) and the U.S. EnvironmentalProtection Agency (EPA) have established U.S. federal rules that setnational greenhouse gas emission standards. Beginning with 2012 modelyear vehicles, automobile manufacturers required that fleet-widegreenhouse gas emissions be reduced by approximately five percent everyyear. Included in the requirements, for example, the new standardsdecreed that new passenger cars, light-duty trucks, and medium-dutypassenger vehicles had to have an estimated combined average emissionslevel no greater than 250 grams of carbon dioxide (CO₂) per mile invehicle model year 2016.

Catalytic converters are used in internal combustion engines to reducenoxious exhaust emissions arising when fuel is burned as part of thecombustion cycle. Significant among such emissions are carbon monoxideand nitric oxide. These gases are dangerous to health but can beconverted to less noxious gases by oxidation respectively to carbondioxide and nitrogen/oxygen. Other noxious gaseous emission products,including unburned hydrocarbons, can also be converted either byoxidation or reduction to less noxious forms. The conversion processescan be effected or accelerated if they are performed at high temperatureand in the presence of a suitable catalyst being matched to theparticular noxious emission gas that is to be processed and converted toa benign gaseous form. For example, typical catalysts for the conversionof carbon monoxide to carbon dioxide are finely divided platinum andpalladium, while a typical catalyst for the conversion of nitric oxideto nitrogen and oxygen is finely divided rhodium.

Catalytic converters have low efficiency when cold, i.e. the runningtemperature from ambient air start-up temperature to a temperature ofthe order of 300 C or “light-off” temperature, being the temperaturewhere the metal catalyst starts to accelerate the pollutant conversionprocesses previously described. Below light-off temperature, little tono catalytic action takes place. This is therefore the period during avehicle's daily use during which most of the vehicle's pollutingemissions are produced. Getting the catalytic converter hot as quicklyas possible is important to reducing cold start emissions.

BRIEF DESCRIPTION OF THE DRAWING

For simplicity and clarity of illustration, elements illustrated in theaccompanying figure are not drawn to common scale. For example, thedimensions of some of the elements are exaggerated relative to otherelements for clarity. Advantages, features and characteristics of thepresent invention, as well as methods, operation and functions ofrelated elements of structure, and the combinations of parts andeconomies of manufacture, will become apparent upon consideration of thefollowing description and claims with reference to the accompanyingdrawings, all of which form a part of the specification, wherein likereference numerals designate corresponding parts in the various figures,and wherein:

FIG. 1 is a perspective outline view of a catalytic converter brickbeing formed in an extrusion process.

FIG. 2 is a longitudinal sectional view of a known form of catalyticconverter.

FIG. 3 is a longitudinal sectional view of a catalytic converterassembly according to an embodiment of the invention.

FIG. 4 is a cross-sectional view of a catalytic converter according toanother embodiment of the invention.

FIG. 5 is a cross-sectional view of a fragment of a catalytic convertersubstrate according to an embodiment of the invention.

FIG. 6 is a longitudinal sectional view of the substrate fragmentillustrated in FIG. 5 taken on the line B-B of FIG. 5.

FIG. 7 is a perspective end view of a larger fragment corresponding tothe small substrate fragment shown in FIGS. 5 and 6.

FIG. 8 is a perspective end view similar to FIG. 7 but showing acatalytic converter substrate according to another embodiment of theinvention.

FIG. 9 is a side view of a wire insert for use in a catalytic convertersubstrate of the form shown in FIG. 8.

FIG. 10 is a longitudinal sectional view of a fragment of a catalyticconverter substrate showing the wire insert of FIG. 9 inserted into thesubstrate.

FIG. 11 is a longitudinal sectional view of a fragment of a catalyticconverter substrate showing an inserted wire insert according to anotherembodiment of the invention.

FIG. 12 is a cross-sectional view of a fragment of a catalytic convertersubstrate according to a further embodiment of the invention.

FIG. 13 is a longitudinal sectional view of the substrate fragmentillustrated in FIG. 12.

FIG. 14 is a perspective end view of a fragment of a catalytic convertersubstrate and emitter and collector electrodes illustrating anembodiment of the invention.

FIG. 15 is a perspective end view of a fragment of a catalytic convertersubstrate and emitter and collector electrodes illustrating analternative embodiment of the invention.

FIG. 16 is a perspective end view of a fragment of a catalytic convertersubstrate and collector electrode illustrating a further embodiment ofthe invention.

FIG. 17 is a perspective end view of fragments of a catalytic convertersubstrate and emitter electrode and, to a larger scale, a collectorelectrode, illustrating another embodiment of the invention.

FIG. 18 is a schematic view of a control system according to anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING THE PRESENTLY PREFERREDEMBODIMENTS

A catalytic converter may take any of a number of forms. Typical ofthese is a converter having a cylindrical substrate of ceramic material,generally called a brick, an example of which is shown in FIG. 1. Thebrick 10 has a honeycomb structure in which a number of small areapassages or cells 12 extend the length of the brick, the passages beingseparated by walls 14. There are typically from 400 to 900 cells persquare inch of cross-sectional area of the substrate unit and the wallsare typically in the range 0.006 to 0.008 inches in thickness. Asindicated in FIG. 1, the ceramic substrates are formed in an extrusionprocess in which green ceramic material is extruded through anappropriately shaped die and units are cut successively from theextrusion, the units being then cut into bricks which are shorter than aunit. The areal shape of the passages 12 may be whatever is convenientfor contributing to the overall strength of the brick while presenting alarge contact area at which flowing exhaust gases can interact with ahot catalyst coating the interior cell walls.

The interiors of the tubular passages in the bricks are wash-coated witha layer containing the particular catalyst material. A suitablewash-coat contains a base material, suitable for ensuring adherence tothe cured ceramic material of the substrate, and entrained catalystmaterial for promoting specific pollution-reducing chemical reactions.Examples of such catalyst materials are platinum and palladium which arecatalysts effective in converting carbon monoxide and oxygen to carbondioxide, and rhodium which is a catalyst suitable for converting nitricoxide to nitrogen and oxygen. Other catalysts are known which promotehigh temperature oxidation or reduction of other gaseous materials. Thewash-coating is prepared by generating a suspension of the finelydivided catalyst in a ceramic paste or slurry, the ceramic slurryserving to cause the wash-coat layer to adhere to the walls of theceramic substrate. As an alternative to wash-coating to place catalystmaterials on the substrate surfaces, the substrate material itself maycontain a catalyst assembly so that the extrusion presents catalystmaterial at the internal surfaces bounding the substrate passages orcells.

A catalytic converter may have a series of such bricks, each having adifferent catalyst layer depending on the particular noxious emission tobe neutralized. Catalytic converter bricks may be made of materialsother than fired ceramic, such as stainless steel. Also, they may havedifferent forms of honeycombed passages than those described above. Forexample, substrate cells can be round, square, hexagonal, triangular orother convenient section. In addition, if desired for optimizingstrength and low thermal capacity or for other purposes, some of theextruded honeycomb walls can be formed so as to be thicker than other ofthe walls, or formed so that there is some variety in the shape and sizeof honeycomb cells. Junctions between adjacent interior cell walls canbe sharp angled or can present curved profiles.

Typically, as shown in FIG. 2, the wash-coated ceramic honeycomb brick10 is wrapped in a ceramic fibrous expansion blanket 16. A stamped metalcasing or can 18 transitions between the parts of the exhaust pipe foreand aft of the catalytic converter so as to encompass the blanketwrapped brick. The casing 18 is typically made up of two parts which arewelded to seal the brick in place. The expansion blanket provides abuffer between the casing and the brick to accommodate their dissimilarthermal expansion coefficients. The sheet metal casing expands manytimes more than the ceramic at a given temperature increase and if thetwo materials were bonded together or in direct contact with each other,destructive stresses would be experienced at the interface of the twomaterials. The blanket also dampens vibrations from the exhaust systemthat might otherwise damage the brittle ceramic.

In use, the encased bricks are mounted in the vehicle exhaust line toreceive exhaust gases from the engine and to pass them to the vehicletail pipe. The passage of exhaust gases through the catalytic converterheats the brick to promote catalyst activated processes where theflowing gases contact the catalyst layer. Especially when the vehicleengine is being run at optimal operating temperature and when there issubstantial throughput of exhaust gases, such converters operatesubstantially to reduce the presence of noxious gaseous emissionsentering the atmosphere. Such converters have shortcomings however atstart-up when the interior of the brick is not at high temperature andduring idling which may occur frequently during city driving or whenwaiting for a coffee at a Tim Hortons drive-through.

Converter shape, profile and cell densities vary among differentmanufacturers. For example, some converter bricks are round and some areoval. Some converter assemblies have single stage bricks that aregenerally heavily wash-coated with the catalyst metals, while others mayhave two or three converter bricks with different wash-coatings on eachbrick. Some exhausts have 900, 600 and 400 cell per square inch (cpsi)cell densities used in the full exhaust assembly, while others use only400 cpsi bricks throughout. A close-coupled converter may be mounted upclose to the exhaust manifold with a view to reducing the period betweenstart-up and light-off. An underfloor converter can be located furtherfrom the engine where it will take relatively longer to heat up but berelatively larger and used to treat the majority of gases once theexhaust assembly is up to temperature. In another configuration, a unitfor reducing the period to light-off and a unit to deal with high gasflow after light-off are mounted together in a common casing.

At one or more locations in the converter assembly, sensors are mountedin the exhaust gas flow provides feedback to the engine control systemfor emission checking and tuning purposes. Aside from start-up, controlof fuel and air input has the object typically of maintaining a 14.6:1air:fuel ratio for an optimal combination of power and cleanliness. Aratio higher than this produces a lean condition—not enough fuel. Alower ratio produces a rich condition—too much fuel. The start-upprocedure on some vehicles runs rich for an initial few seconds to getheat into the engine and ultimately the catalytic converter. Thestructures and operating methods described below for indirectly heatingthe catalyst layers and the exhaust gases can be used with each of aclose-coupled catalytic converter, an underfloor converter, and acombination of the two.

FIG. 3 shows an assembly having two bricks of the sort illustrated inFIGS. 1 and 2, but in which one brick is modified to enable inductionheating. Induction heating is a process in which a metal body is heatedby applying a varying electromagnetic field so as to change the magneticfield to which the metal body is subject. This, in turn, induces eddycurrents within the body, thereby causing resistive heating of the body.In the case of a ferrous metal body, heat is also generated by ahysteresis effect. When the non-magnetized ferrous metal is placed intoa magnetic field, the metal becomes magnetized with the creation ofmagnetic domains having opposite poles. The varying field periodicallyinitiates pole reversal in the magnetic domains, the reversals inresponse to high frequency induction field variation on the order of1,000s to 1,000,000s cycles per second (Hz) depending on the material,mass, and shape of the ferrous metal body. Magnetic domain polarity isnot easily reversed and the resistance to reversal causes further heatgeneration in the metal.

As illustrated in FIG. 3, surrounding the ceramic substrate is a metalcoil 20 and, although not shown in the figure, located at selectedpositions within the ceramic substrate 10 are metal elements which maytake any of a number of forms. By generating a varying electromagneticfield at the coil 20, a chain reaction is initiated, the end result ofwhich is that after start-up of a vehicle equipped with an exhaustsystem embodying the invention, light-off may be attained more quicklyin the presence of the varying electromagnetic induction field than ifthere were no such field. The chain reaction is as follows: the varyingelectromagnetic field induces eddy currents in the metal elements; theeddy currents cause heating of the metal elements; heat from the metalelements is transferred to the ceramic substrate 10; heat from theheated substrate is transferred to exhaust gas as it passes through theconverter; and the heated exhaust gas causes the catalytic reactions totake place more quickly compared to unheated exhaust gas.

The coil 20 is a wound length of copper tube, although other materialssuch as copper or litz wire may be used. Copper tube is preferredbecause it offers high surface area in terms of other dimensions of thecoil; induction being a skin-effect phenomenon, high surface area is ofadvantage in generating the varying field. If litz wire or copper wireis used, an enamel or other coating on the wire is configured not toburn off during sustained high temperature operation of the converter.

A layer of 22 of electromagnetic field shielding material such asferrite is located immediately outside the coil 20 to provide aninduction shielding layer and reduces induction loss to the metalconverter housing 18. The ferrite 22 also acts to increase inductivecoupling to the ceramic substrate 10 to focus heating.

The coil is encased in cast and cured insulation 24. The cast insulationfunctions both to stabilize the coil position and to create an air-tightseal to confine passage of the exhaust gases through the ceramichoneycomb substrate 10 where the catalytic action takes place. Theinsulation 24 also provides a barrier to prevent the induction coil 20from shorting on the converter can 18 or the ferrite shield 22. Theinsulation is suitable alumino-silicate mastic. In an alternativeembodiment, the converter is wrapped in an alumino-silicate fibre paper.In one manufacturing method, the copper coil 20 is wrapped around theceramic substrate 10 and then placed in the converter casing or can 18.In an alternative manufacturing method, the coil 10 is placed in the can18 and the ceramic substrate 10 is inserted into the coil can assembly.

In one embodiment of the invention, a varying electromagnetic inductionfield is generated at the coil by applying power from either a DC or ACsource. Conventional automobiles have 12 VDC electrical systems. Theinduction system can operate on either DC or AC power supply. Theinduction signal produced can also be either DC or AC driven. For eitherDC or AC, this produces a frequency of 1 to 200 kHz, a RMS voltage 130to 200V and amperage of 5 to 8 A using 1 kw of power as an example. Inone example suitable for road vehicles, a DC to DC bus converts thevehicle's 12 VDC battery power to the required DC voltage outlinedabove. In another example suitable for conventional road vehicles, a DCto AC inverter converts the vehicle's 12V DC battery power to thedesired AC voltage outlined above. Another example is more suited tohybrid vehicles having both internal combustion engines and electricmotors have on-board batteries rated in the order of 360V voltage and 50kW power. In this case, the battery supply power is higher, but the samebasic DC to DC bus or DC to AC inverter electrical configuration can beapplied. An IGBT high speed switch is used to change the direction ofelectrical flow through the coil. In terms of the effect of a varyingelectromagnetic induction field on metal in the ceramic substrate, a lowswitching frequency produces a longer waveform providing good fieldpenetration below the surface of the metal element and thereforerelatively uniform heating. However, this is at the sacrifice of hightemperature and rapid heating owing to the lack of switching. Incontrast, a high switching frequency produces a shorter waveform, whichgenerates higher surface temperature at the sacrifice of penetrationdepth. Applied power is limited to avoid the risk of melting the metalelements. A suitable power input to a single brick coil is of the orderof 1.1 kw.

As previously described, metal elements are located at selectedlocations of the ceramic substrate 10. For two identical metal elements,generally, a metal element closer to the source of the induction fieldbecomes hotter than an equivalent metal element located further awayfrom the source because there is an increase in efficiency; i.e. thelevel of induction achieved for a given power input. With a regularinduction coil 10 as illustrated, metal elements at the outside of thecylindrical substrate 10 are near to the coil 20 and become very hot,while an equivalent metal element near the substrate center remainsrelatively cool. An air gap 26 between the coil 10 and the nearestinductance metal elements prevents significant heat transfer from theinductance metal elements to the coil which would otherwise increase thecoil resistivity and so lower its efficiency. In an alternativeembodiment, a relatively higher concentration of the metal elements issited towards the center of the ceramic substrate to compensate for thefact that the field effect from the coil source is considerably lessnear the centre of the substrate than near the outer part of thesubstrate. In a further embodiment, a relatively higher metal elementload is located at some intermediate position between the centre andperimeter of the ceramic substrate, whereby heat generated within theintermediate layer flows both inwardly to the center and outwardly tothe perimeter for more efficient overall heating. The induction coil 20is sized to the metal load to achieve high efficiency in terms ofgenerating heat and in terms of speed to light-off.

The electromagnetic induction field can be tuned to modify heatingeffects by appropriate selection of any or all of (a) the electricalinput waveform to the coil, (b) nature and position of passive fluxcontrol elements, and (c) nature, position, and configuration of thecoil 20. For example, the induction field is tuned to the location ofmetal elements or to the location of high concentration of such elementsin the ceramic substrate 10. Alternatively, or in addition, the appliedfield is changed with time so that there is interdependence between theinduction field pattern and the particular operational phase frompre-start-up to highway driving. In an alternative configuration, morethan one coil can be used to obtain desired induction effects. Forexample, as shown in the cross sectional view of FIG. 4, the ceramicsubstrate 10 has an annular cross-section with a first energizing coil10 at the substrate perimeter and a second energizing coil at thesubstrate core.

As shown in the fragmentary sectional views of FIGS. 5 and 6, in oneembodiment of the invention, the metal elements are metal particles 28which are embedded in the walls 14 of the ceramic honeycomb substrate,the particle size being less than the width of walls 14. As part of themanufacturing process, the metal particles are added and mixed with aceramic base material while the ceramic is still green or flowable; i.e.before it is extruded. In this way, the particles are distributedrelatively evenly throughout the ceramic base material to be extruded.In operation of this embodiment, when a varying electromagneticinduction field is applied from the coil 20, the ceramic material in thesubstrate is comparatively invisible to the applied field and thereforedoes not heat up. The metal particles 28 heat up and conduct heat to thewalls 14 of the ceramic honeycomb within which they are bound.

In an alternative manufacturing embodiment, mixing of the ceramic basematerial with metal particles and subsequent extrusion of the mixture toform the honeycomb substrate are configured so that selected locationsin the substrate have a greater metal particle concentration than otherlocations. Such a configuration may be attained by bringing together atthe extruder several streams of green ceramic material, with the streamshaving different levels of metal content from one another. The streamsare then fused immediately before extrusion so that the variation inmetal content is mirrored across the cross-section of the extrudedsubstrate. In a further embodiment, metal particles are used that areelongate or otherwise asymmetric so that they tend to align somewhatcloser to converter cell walls in the course of the extrusion process.In another embodiment, the particle lengths are made sufficiently longthat at least some adjacent particles come into electrical contact witheach other in the course of mixing or subsequent extrusion.

In alternative embodiments of the invention, the metal elements arelocated within the ceramic honeycomb structure, but not embedded withinthe material of the honeycomb structure itself. For example, duringpost-processing of ceramic substrate bricks, metal elements arepositioned in selected cells 12 of the substrate 10. In oneimplementation as illustrated in FIG. 7, a high concentration of metalparticles is mixed with a mastic and the resulting mixture is injectedusing a method such as that described in copending utility patentapplication 13971129 (A catalytic converter assembly and process for itsmanufacture), filed Aug. 20, 2013, the disclosure of which applicationis incorporated herein by reference in its entirety and made part of thepresent application for all purposes. Following injection, injectedthreads 30 of the mastic mixture is cured by, for example, microwaveheating as described in copending utility patent application 13971247 (Acatalytic converter assembly and process for its manufacture) filed Aug.20, 2013, the disclosure of which application is also incorporatedherein by reference in its entirety and made part of the presentapplication for all purposes. In one implementation, the mastic basematerial is a low viscosity, paste-like mixture of glass fibers, clayslurry, polymer binder and water, from which the water and the organicbinder are driven off in the course of the curing process. Followingcuring, the injected threads 30 are predominantly silica in a porousmatrix of silica, ceramic and metal particles.

In another exemplary configuration (not shown), selection of passages 12to be injected is made so that the threads of cured mastic metal mixtureare not uniformly distributed, but generally occupy an intermediateannular zone of the cylindrical substrate. In the operation of such astructure, heat is preferentially generated at the annular zone and istransferred from the zone sites inwardly towards the substrate core andoutwardly towards its perimeter. It is preferred that metal particleswithin the mastic metal mixture injected into a cell are predominantlysituated close to the cell interior surface rather than towards the cellcenter so as to localize heat generation near the cell surfaces and toget greater heat transfer and speed of such transfer to the ceramicsubstrate. Appropriately directed agitation of the loaded converterbrick after during and/or after extrusion and before curing canencourage some migration of metal particles towards the cell walls.

In injected cell implementations, any cell which is blocked with athread of the mastic and metal particles cannot function to catalyze apollution-reducing reaction as exhaust gas passes through the cell. Sucha plugged cell is used solely for heating at start-up or when idling.Consequently, only selected ones of the cells are filled with thecomposite heating material. In the example illustrated, the substratehas 400 cells per square inch. Of these, from 8 to 40 cells per squareinch are filled with the metal mastic composite depending on the radialposition of the cells and such that over the full areal extent of thesubstrate, the blocked cells occupy from 2 to 10% of the substrate area.

In a further embodiment of the invention, discrete metal elements thatare larger than the particle sizes discussed with the FIG. 7 embodimentare inserted at selected cell locations in the catalytic convertersubstrate. As shown in FIG. 8, exemplary metal elements are wires 32which are positioned within selected substrate cells and which extendalong the full length of the cells from the brick entrance to its exit.The inserted wires 32 may, for example, be of round, square or othersuitable cross-section. As shown in the FIG. 8 embodiment, the ceramicconverter substrate 10 has square cells and round section wires. Squaresection wires provide better heat transfer to the square section cellsdue to high contact area between the two materials. However, roundsection wires are easier to insert into the square section cells owingto there being less surface area contact causing insertion resistance.The wires may be fixed into their respective cells by a friction fitwhich is at least partially achieved by closely matching the wireexterior area dimensions to the cell area dimensions so that surfaceroughness of the wire surface and the cell walls locks the wires inplace. Wire is drawn to be from 0.002 inches to 0.005 inches less inwidth than the cell width to enable insertion.

In one configuration, a wire insert 34 is formed to have a bow-shape asshown in FIGS. 9 and 10. The bowed wire 34 has memory so that after thebow is straightened as the wire is inserted into a cell 12, the insert34 tends to return to its bow shape causing center and end regions ofthe wire to bear against opposed sides or corners of the cell 12 and soenhance the friction fit to retain the wire in place in the cell.Alternatively, or in addition, wires 36 are crimped at their ends asshown in the embodiment of FIG. 11 so as to establish end bearingcontact sites. The overall friction fit in each case is such as toresist gravity, vibration, temperature cycling, and pressure on thewires as exhaust gases pass through the converter.

Wires may alternatively, or in addition, be fixed into the cells bybonding outer surfaces of the wires to interior surfaces of respectivecells. In exemplary bonding processes, the wire is at least partiallycoated with an adhesive/mastic before insertion, or a small amount ofadhesive/mastic is coated onto the cell interior walls before wireinsertion. High temperature mastic materials and composite adhesives areused. Suitable mastic, for example, is of the same form as that used inthe injection embodiments previously described. A composite adhesive,for example, is a blend of ceramic and metal powders with a bindertransitioning between the two main materials. Such a blend is used tominimize temperature cycling stress effects in which there may besignificant metal wire expansion/contraction, but vanishingly smallexpansion/contraction of the ceramic substrate. This differential canproduce stresses at the adhesive interface between the two materials. Byusing such a composite adhesive, movement of a bonded wire relative tothe surrounding cell surface is minimized and heat transfer increasedheat transfer is obtained by the presence of the composite adhesivematerial.

As shown in the embodiment of FIG. 8, an array of wires having a uniformdistribution through the array of converter cells is used. In oneexample, 1 wire is inserted for every 25 cells of a 400 cpsi substrate.This has a satisfactory heating performance and not too great anocclusion of converter cells from the viewpoint of pollution-cleaningcatalytic reactions implemented at the converter. A significantly higherratio of wires to cells can result in slower heating to light-offbecause of the high overall thermal capacity represented, in total, bythe wires and because of the fact that some wires block the “line ofsight” field effect on other wires. In contrast, while a significantlylower ratio of wires to cells results in fewer occlusions of convertercells, a sparse distribution of metal of the order of less than 1 wireinserted for every 49 cells in a 400 cpsi substrate results in reducedheat generation and increased time to light-off. As in the case of theinjected metal particle embodiments described previously, wires can beinserted in a non-uniform pattern: for example, to a generally annularconcentration of wire insertions at an intermediate radial positionwithin the ceramic converter substrate; or to position a greaterconcentration of wires near the core of the converter furthest from thecoil compared to the concentration of wires near the perimeter of theconverter.

There are advantages and disadvantages as between using metal particlesand larger metal elements such as wire inserts. Induction heatingproduces a “skin-effect” hot surface of the metal being heated. Thismakes the surface area of the metal element important to efficientheating. Generally, the more surface area there is, the quicker themetal heats-up. However, induction is a line-of-sight process where thesurface that “sees” the inductive field is the one that heats-up firstand gets hotter. Powder particles heat-up quickly and larger bodiesheat-up more slowly. In the case of particles, whether dispersed andembedded in the ceramic substrate material itself or in mastic injectedinto selected cells, each particle acts independently of the next sothere is little conduction between neighbouring particles. Consequently,heat distribution may be relatively poor. Larger metal bodies conductheat well throughout their bulk and so are preferred in terms ofdistributing heat. The thin wire embodiments of FIG. 8 offer a goodcompromise between particles and solid bodies in terms of surface area,line-of-sight positioning and conduction characteristics all of whichsignificantly affect the heating performance.

Conduction is the primary source of heat transfer to the ceramicsubstrate and therefore to the exhaust gases when the converter is inoperation. In the case of the wire insert embodiments, there is also asmall amount of convective heat transfer but this is limited as there isonly a small air gap between the wires and the interior surface of thecells so air movement is minimized. There is also a relatively smallamount of radiation heat transfer in the case such as inserted wireswhere the wires are separated over a large part of their surface areafrom the interior of the cells but where the separation is not occluded.

As previously described and illustrated, a preferred distribution ofinductance metal elements relative to the position of cells isconfigured so that the heating effect is generally uniform across thearea of the converter. Especially for start-up and idling, wherenon-uniform exhaust gas flow patterns may develop, there may beadvantage in deliberately developing a heat pattern across the converterwhich is not uniform. As previously noted, this may be achieved byappropriately siting inductance metal elements in selected cells. It mayalso be achieved in another embodiment of the invention by usingdifferently sized or shaped metal inserts or by using differentconcentrations of particles in the injection embodiments. It may beachieved in a further alternative structure and method by generating anon-radially symmetrical field or generating two or more interferingfields. Such induction fields and their interaction could, for example,be varied in the period from start-up to light-off. Changing heatingeffects may also be achieved using a combination of such inductancemetal siting and field manipulation. Targeted heating that varies inposition, time, or both can be implemented with a view to increasingconversion of pollutants, to saving power, or for other reasons.

In another embodiment of the invention, the metal elements are notentrained within the material of the ceramic substrate and are notinjected or positioned into selected cells. Instead, as shown in thefragmentary section views of FIGS. 12 and 13, a ferrous metal coating 38is formed on the interior surfaces of walls 14 of selected convertercells before application of the catalyst(s) coating 40. Alternatively,(not shown) the ferrous metal coating is laid down as a common coatingwith the catalyst metal(s), either by using alloy particles that containboth the ferrous metal and the catalyst metal(s) or by having a wash inwhich both the ferrous metal particles and the catalyst metal particlesare dispersed. In the latter arrangements, there may be some loss ofcatalyst action arising from the ferrous metal taking some of thecatalyst metal sites and so a compromise is necessary.

All metals are responsive to some extent to an induction field, withferrous metals being the materials most readily heated by such a field.Catalyst materials contained within a wash coat applied to a honeycombsubstrate cell interior are typically platinum group metals—platinum,palladium and rhodium. Such materials have a low magnetic permeabilityof the order of 1×10⁶ (in the case of platinum) and so are influencedonly very slightly by an applied induction field. Moreover, catalystmetals are present in very tiny amounts of the order of a gram perconverter brick so there is insufficient metal in the catalyst assemblyto generate and transfer any noticeable heat to the ceramic substrate instart-up period or idling periods. In contrast, ferrous metals used forthe induction heating are present in an amount of the order of 60 to 200grams per brick and have magnetic permeability of the order of 2.5×10⁻¹in the case of iron.

As previously indicated, induction heating is applied in the periodbefore light-off in order to reduce the amount of harmful pollutantswhich are emitted before the catalyst coatings have reached atemperature at which they start to catalyse reactions in which thepollutants are converted to more benign emissions. Particularly for citydriving, engine operation is frequently characterized by bursts ofacceleration and braking punctuated by periods of idling. At such times,the temperature of the exhaust gas entering the converter and the wallsof the substrate with which the flowing exhaust gas is in contact maystart to fall. If the idling and the cooling continue, the temperatureof the substrate and the gas fall below that required for thepollutant-reducing catalytic reactions to occur. In such periods,heating of the converter substrate is obtained by switching on theinduction heating. At a future point, when the vehicle is no longeridling and the exhaust gas temperature increases past the temperaturerequired for effective catalytic reaction to convert the toxic exhaustgas pollutants to relatively benign products, the induction heating isswitched off.

Embodiments of the induction heating invention have been described inthe context of ferrous alloys such as steel which are commerciallyavailable in common shapes and sizes, and at reasonable cost.Alternative ferromagnetic metals such as cobalt or nickel or theiralloys may also be used. The metal used must survive high temperaturereached by the catalytic converter and repeated temperature cycling asthe metal intrusions move repeatedly from a cold start to operatingtemperature and back again. Generally, alloying of iron or otherferromagnetic metal gives advantageous mechanical and physicalproperties such as corrosion/oxidation resistance, high temperaturestability, elastic deformation, and formability.

Referring to FIGS. 14 to 17, embodiments of the invention areillustrated which are adapted for electrohydrodynamic (EHD) heat andmass transfer of exhaust gas passing through the passages or cells of acatalytic converter substrate. In the EHD process, free electrons aregenerated and caused to migrate from a charged upstream emitter to agrounded downstream collector 44. In the course of their migration,electrons collide with molecules in the exhaust gas, transferringmomentum to the gas molecules and causing turbulence in the gas flow.This means that there is a lesser tendency for the gas flow through thecells to adopt a laminar flow and/or there is a tendency for a laminargas flow to depart from laminarity. Both tendencies bring more exhaustgas into contact with the walls of the converter substrate cell wallsthan would be the case without EHD stimulation. This results in both anincrease in heat transfer between the exhaust gas and the walls of thesubstrate and an increase in the catalytic pollution-reducing reactionsowing to increased contact of the exhaust gas with hot catalyst at theinterior surfaces of the substrate cell walls.

In operation, in the period between start-up and light-off, thesubstrate walls are at a lower temperature than the exhaust gas. Moreheat is transferred from the flowing exhaust gas to the substrate bystimulation of EHD heat transfer stimulation and the substratetemperature increases at a faster rate than would be the case withoutthe EHD heating process. A control circuit includes a first temperaturesensor to monitor the temperature of the converter substrate and asecond temperature sensor to monitor the temperature of the exhaust gasimmediately upstream of the converter. The control circuit includes acomparator for measuring the difference between the exhaust gas and theconverter substrate temperatures and a switch controlled by thecomparator to switch on EHD voltage to the emitter. Greater speed tolight-off is obtained by switching in the EHD heat transfer process tostimulate heat transfer from the exhaust gas during the start-up tolight-off period. At a future point, when the substrate is sufficientlyhot to cause the pollution reducing catalytic reaction to occur, EHDheat transfer stimulation is switched off.

In addition, during idling periods, the temperature of the exhaust gasentering the converter may start to drop and a situation may arise wherethe catalytic converter substrate walls are still at an optimaltemperature for catalyst reactions, but the gas entering the converteris below a temperature that it is optimal for such reactions. During theidling phases, the converter may remain at or near an optimal operatingtemperature from the viewpoint of reducing harmful emissions, even asthe gas flowing through the converter is cooling down. In such periods,low power heating of the cooling exhaust gas is obtained by switching inthe EHD heat transfer process to draw heat for a limited period of time.At a future point, when the vehicle is no longer idling and the exhaustgas temperature increases past the monitored substrate temperature, theEHD heat transfer stimulation can be switched off.

Referring in detail to FIG. 14, for operating a catalytic converter inwhich EHD is implemented, an emitter 42 is connected to a 25 to 50kilovolts power source delivering very low amperage, the systemtherefore consuming only a few watts and a collector 44 is grounded. Theflow of electrons produces preferential heat exchange between thecharged exhaust gas and the converter substrate compared with thepassage through the catalytic converter of uncharged exhaust gas. Theconductivity of the exhaust gas influences the extent of mixing and flowchanges that, in turn, cause more rapid heat transfer between theconverter substrate and the exhaust gas. Generally, the more conductivethe exhaust gas, the higher the turbulent effect and the greater the EHDheat transfer effect.

As shown in the FIG. 14 embodiment, in a first emitter collectorarrangement, the emitter 42 is a regular mesh of 0.25 inch diameter rodsand 0.375 inch apertures, the mesh mounted immediately upstream of theconverter brick 10. A collector 44 is a similar metal mesh locatedimmediately downstream of the converter brick, this mesh being connectedto ground. Interconnection of the upstream mesh to a positive voltagesource and interconnection of the downstream mesh to ground provides thepositive (emitter) and negative (collector) electrodes required togenerate electron flow.

As shown in FIG. 15, in a second emitter collector arrangement, aconfiguration of wire inserts is used similar to that shown in FIG. 8except that the wire inserts are interconnected to each other and toground. In the illustrated configuration, a continuous wire 46 is usedand is looped in and out of substrate cells so that adjacent wireinserts are effectively stitched into place.

In another embodiment, as shown in FIG. 16, the mesh collector 44 hasprotruding wires 48 that are aligned with the longitudinal axis ofselected substrate cells. In the course of manufacture, the protrudingwires 48 of the mesh collector 44 are slid back towards the front end ofthe converter brick and into the aligned cells 12. The mesh collector islocked to the back side of the substrate. In one form, the protrudingwires 48 have a friction fit within the selected cells 12 as previouslydescribed with reference to FIGS. 8 to 11 or are secured in place usinga suitable adhesive. In another form and associated method, theprotruding wires are pre-located in the selected cells and then bound inplace by injecting a metal mastic matrix into the cell and then dryingand sintering the matrix.

In a further emitter collector arrangement as shown in FIG. 17, theemitter 42 is a metal sphere having a diameter matching the diameter ofa cylindrical converter substrate, the sphere being devoid of angularcorners so that electron emission is relatively evenly distributedacross its surface. A series of collectors are formed by fillingselected converter cells 12 with a metal powder in a binder matrix toconstitute a series of collector sites 30, the collector thread withinthe plugged cells being connected together and to ground by, forexample, a mesh of the form shown in FIG. 16 but with relatively shortercontact projections 48. The metal particles are mixed with a mastic andthe resulting mixture is injected using a method such as that describedin copending utility patent application 13971129 (A catalytic converterassembly and process for its manufacture), filed Aug. 20, 2013, thedisclosure of which application is incorporated herein by reference inits entirety and made part of the present application for all purposes.Following injection, injected threads 30 of the mastic mixture are curedby, for example, microwave heating as described in copending utilitypatent application 13971247 (A catalytic converter assembly and processfor its manufacture) filed Aug. 20, 2013, the disclosure of whichapplication is also incorporated herein by reference in its entirety andmade part of the present application for all purposes. In oneimplementation, the mastic base material is a low viscosity, paste-likemixture of glass fibers, clay slurry, polymer binder and water, fromwhich the water and the organic binder are driven off in the course ofthe curing process. Following curing, the injected threads 30 arepredominantly silica in a porous matrix of silica, ceramic and metalparticles.

In a modification (not shown) of the FIG. 17 embodiment, a uniformlydistributed first selection of cells is blocked with the metal bindermatrix, the cells being wired together and to each other to formemitters. An equal number of cells generally alternating in distributionwith the emitter cells are also blocked with metal binder matrix, thesecond set of cells being wired together and to ground to formcollectors. This arrangement has high efficiency at the surface ofsubstrate cells because the emitter and collector are integral parts ofthe substrate.

In further alternatives, the emitter and collector configurations shownpreviously can be matched differently.

A benefit of induction heating is that converter assemblies can besmaller. A cold start produces 75 to 90% of the pollutants of aninternal combustion engine and this drives the size of the overallexhaust assemblies. Since the induction heating technology addressesmuch of this 75 to 90%, there is the ability to shrink the converterpackage. By introducing added heat and mass transfer with theimplementation of an EHD sub-system, further size reduction is possible.

National emissions standard requirements are a prime driver forcatalytic converter design. The requirements are very high and difficultto meet by with a single converter. Currently, therefore, most cars nowin production employ a two converter assembly—one at a close-coupledposition and the other at an underfloor position. The close-coupledconverter is normally lighter in weight than the underfloor converterwhich means that is has low thermal capacity and so will attain acatalytic reaction operating temperature as quickly as possible.However, the close-coupled converter is of relatively lower efficiencycompared with the heavier underfloor converter once the two convertershave reached their respective catalytic reaction operating temperatures.By introducing induction heating to the exhaust process at start-up, itmay be manufacturers can return to a single converter installation andmeet emission standards by eliminating the need for the close-coupledconverter.

Although embodiments of the invention have been described in the contextof ceramic catalytic converter substrates, stainless substratesubstrates can also be used, with induction heating being implemented ina similar way to that described above. Substrates made of 400 seriesmagnetic alloys are preferred because such alloys exhibit significantmagnetic hysteresis. With a surrounding coil, the outer annular regionsof small diameter stainless steel substrates heat up extremely quicklyowing to their small thermal capacity.

In the case of EHD heat and mass transfer, in an alternative embodimentof the invention using a stainless steel substrate, the catalyticconverter has two steel bricks with the first functioning as an emitterand the second as a collector. In such cases, insertion of wire insertsor injection and curing of metal mastic threads are obviated because thesteel bricks themselves function to emit and collect the free electrons.

Embodiments of the EHD heat and mass transfer invention have beendescribed in the context of ferrous alloys such as steel which arecommercially available in common shapes and sizes, and at reasonablecost. Alternative metals may be used for the EHD electrodes providedthat they can survive high temperature reached in the catalyticconverter and repeated temperature cycling as the metal elements in theconverter substrate body move repeatedly from a cold start to operatingtemperature and back again. Generally, alloying gives advantageousmechanical and physical properties such as corrosion/oxidationresistance, high temperature stability, elastic deformation, andformability.

In applying the induction heating and EHD mass and heat transferinventions to the structure and operation of a catalytic converter, theelectrical circuit and electrical inputs required to implement inductionheating are different from the are electrical circuit and electricalinputs required to implement EHD heat and mass transfer. In thisrespect, it is likely that the EHD effect is influenced by the appliedinduction field. This could be a positive influence with the inductionfield adding a zigzag component to the electron flow resulting inenhanced heat and mass transfer. Alternatively, the induction field mayeclipse the EHD effect.

The induction heating process and the EHD mass and heat transfer processmay be applied simultaneously or at separate times during, or in thecase of induction heating, immediately before start-up. As shown in theschematic view of FIG. 18, one or more temperature sensors 50 mounted inthe catalytic converter are used to monitor temperature at any time andcan be suitably deployed to monitor temperature at different locationsin the converter. Outputs from the temperature sensors are taken to acontroller 52 at which the monitored temperature or temperatures areused through switches 54 to control the times at which the induction andEHD processes are used. Using an appropriate algorithm implemented atthe controller 52, the monitored temperatures may also be used tocontrol specific effects of the applied induction and EHD processeses inimplementations where the induction field characteristics or the EHDhigh voltage characteristics are selectible to achieve a particularinduction heating pattern or EHD effect.

What is claimed is:
 1. A catalytic converter component comprising asubstrate body having a plurality of passages therein for the passagetherethrough of exhaust gas, an emitter electrode at an upstreamlocation in the flowing exhaust gas and a collector electrode at adownstream location in the flowing exhaust gas for collecting electronsin the flowing exhaust gas, and an energizing circuit to generateelectrons at the emitter electrode and to receive electrons at thecollector electrode.
 2. A catalytic converter as claimed in claim 1, thesubstrate body made of ceramic material.
 3. A catalytic converter asclaimed in claim 2, at least one of the electrodes being a metal mesh atan end of the substrate body.
 4. A catalytic converter as claimed inclaim 3, the electrode further including metal in at least some of theplurality of passages, the metal electrically connected to the mesh. 5.A catalytic converter as claimed in claim 4, the metal contained in atleast some of the plurality of passages comprises metal particles in abinder, at least some of the particles in a passage electricallyconnected to one another to establish electrical continuity along thepassage.
 6. A catalytic converter as claimed in claim 4, the metalcontained in at least some of the plurality of passages comprising metalbodies mounted in respective ones of said at least some of the pluralityof passages.
 7. A catalytic converter as claimed in claim 6, wherein themetal bodies are lengths of wire, the lengths of wire electricallyconnected to one another.
 8. A catalytic converter as claimed in claim1, the collector electrode being a metal sphere.
 9. A process fortreating exhaust gases in a catalytic converter comprising generatingfree electrons at an emitter electrode located in an exhaust gas flowupstream of a catalytic converter substrate and collecting emittedelectrons at a collector electrode located in the exhaust gas flowdownstream of the catalytic converter substrate, the passage of suchelectrons through the flowing exhaust gas being such as to introduce orincrease turbulence in the flowing exhaust gas.
 10. A process as claimedin claim 8, wherein a voltage in the range 25 to 50 kilovolts is appliedto the emitter electrode and the collector electrode is grounded.
 11. Aprocess as claimed in claim 9, wherein the substrate body is made ofceramic material and at least one of the electrodes is a metal mesh atone end of the substrate body.
 12. A process as claimed in claim 9, theelectrode further including metal in at least some of the plurality ofpassages, the metal electrically connected to the mesh.
 13. A process asclaimed in claim 9, the metal contained in said at least some of theplurality of passages comprises metal particles in a binder, at leastsome of the particles in each passage electrically connected toestablish electrical continuity along the passage.
 14. A process asclaimed in claim 9, the metal contained in at least some of theplurality of passages comprising metal bodies mounted in respective onesof said at least some of the plurality of passages.
 15. A process asclaimed in claim 9, wherein the metal bodies are lengths of wire, thelengths of wire electrically connected to one another.
 16. A catalyticconversion process as claimed in claim 9, further comprising generatingsaid free electron flow when an engine which is the source of theexhaust gas is operating and when the catalytic converter is below apredetermined threshold temperature.
 17. A process for manufacturing acatalytic converter component comprising positioning metal atpredetermined locations in a ceramic substrate body and mounting anemitter electrode and a collector electrode adjacent the ceramicsubstrate body, the emitter collector combination energizable tointroduce free electrons into a vehicle exhaust gas when the vehicleexhaust gas flows through the catalytic converter component.